Planographic printing



Dec. 10, 1963 D. A. NEWMAN 3,113,512

' PLANOGRAPHIC PRINTING Filed Nov. 6, 1953 5b as 147 Z 2171) b r L17 fih-' IN l EN TOR. DOuyZas- A. AZ-gwman ATTORNE Y6 United States Patent OfEice 3,ll3,5l2 Patented Dec. 1G, li-lfiS 3,113,512 PLAVOGRAPHH',IRlNTlNG Douglas A. Newman, Glen (love, Nfifl, assiguor to ColumhiaRibbon and (Iarbon Manufacturing (Iompany, Inc, Glen Cove, N.Y., acorporation of New York Filed Nov. 6, 1%3, Ser. No. 399,451 4 Claims.(Cl. 161-1492) This invention relates to the ant of facsimile printing,and particularly to the production by facsimile printing methods of aninscribed plate or master from which a. large number of duplicates maybe made by a pianographic printing process, and forms a continuation inpart of the invention of my U .8. Patent No. 2,713,322 issued July 26,1955.

Facsimile apparatus, for the purposes of this description, fallsgenerally into two classes. In either case, electrical impulses, whichmay be sent over communication circuits, are used to provide at thereceiving end an exact duplicate of a master image which has beencaused, by suitable photo-electric or other means, to give rise to saidimpulses at the sending end.

In the first form, the impulses at the receiver are transformed intomechanical movement or pressure for actuating a stylus point whichcorrespondingly inscribes the receiving sheet by moving into and out ofcontact therewith or increasing and decreasing the pressure with whichit contacts the same. By means of this form of device, a manifold set,stencil master or image-forming carbon and planographic plate set may bereadily inscribed, so that duplication of the received image offers noserious problems.

The second form of facsimile operation, and the one with which myinvention is concerned, uses electrical impulses produced insubstantially the same fashion as the first form. The receiver, however,differs in that an electrically conductive stylus point is used. Such astylus may be in circuit with an electroconduotive platen, separatedtherefrom by a specially prepared record sheet mounted on the platen forcontinuous contact with the stylus, said sheet being itself electricallyconductive, as illustrated in the patent .to Kline No. 2,251,742. On theother hand the stylus may be connected to a high potential, highfrequency source to form a corona discharge element which acts on aspecially prepared sheet the paper of which is not necessarilyconductive as disclosed in the patents to Cooley No. 1,702,595 andDalton ct al. No. 2,555,321. These sheets have the property of changingtheir appearance, usually their color, in locmities where the dischargeof current through or against them has occurred. By scanning a sheet ofeither type in synchronization with the scanning operation at thesending device, the local electrically-induced color changes in thesheet may be grouped so as to reproduce the original image scanned bythe sending device. This second method of operation is known in the artas facsimile printing, and will be so referred to hereinafter.

While in many cases the production of planographically printed duplicatecopies of the image received on the facsimile printer would bedesirable, no method for producing them directly and without theintervention of a photographer or copying inscriber has been heretoforedevised. The operation of the facsimile device has hence been limited tothe production of single copies, duplicates of which could be had onlyby resorting to the usual expensive and timeconsuming methods whichinvolve recopying of the received inscription by photography orotherwise, or to hectographic copies as disclosed in the patent toDalton et al. No. 2,398,779, the latter copies being by their verynature relatively impermanent.

It is accordingly an object of my invention to provide a method andequipment for the production of a planographic master by means offacsimile printing apparatus, from which master a plurality of duplicatecopies may be made directly.

My invention is concerned with the development of processes andapparatus whereby a planographic printing plate having a base of paperor similar material which is relatively inexpensive and otherwisesuitable for routine duplication processes, may have theoleophilic-hydrophilic balance of its surface locally disrupted to formink-receptive impressions in response to electrical impulses of thecharacter normally employed in facsimile printing apparatus.

My invention comprehends in particular a planographic plate, preferablyhaving a base of paper or the like, constructed in such .a manner thatits planographic surface may be subjected directly to the eiiects ofelectrical impulses and locally altered in such a manner as to providean ink-receptive image thereon.

A feature of the present invention is the discovery that a meresupercoating of hydrophilic adhesive nature applied to facsimile sheetsof known type can be inscribed by usual facsimile printing devices inthe known manner and then used to print copies planographically.

Other features and advantages will hereinafter appear.

In the drawing:

FIGURE 1 is a large scale diagrammatic showing of a portion of afacsimile platen with a sheet according to the present invention shownin section mounted thereon.

FIG. 2 is a section illustrating another embodiment of the sheet of thepresent invention.

FIG. 3 is a view similar to FIG. 1 but illustrating still anotherembodiment of the sheet of the present invention together with analter-native type of facsimile device.

One form of my invention is represented in FIG. 1 wherein is shown aplanographic plate 15b which may be inscribed directly by the stylus 32of an electrical recording device having a conductive drum it} uponwhich the plate 15b is mounted. A source of electrical energy isindicated diagrammatically at 3'3 and has its terminals connected to thestylus 32 and drum 2b respectively. Plate 15b consists of a sheet ofpaper or like material 151] preferably having such properties ofwet-strength and low wet-extensibility as are necessary to its use as aplanographic plate. The sheet 16b has further been treated so that it isprimarily oleophilic and hydrophobic in char acter, and likewiseelectrically conductive. A carbon, silver or aluminum impregnated paperwhich has been treated to give it suitable wet-strength andWet-extensibility characteristics may profitably serve as the basis forthe plate 1151) about to be described. Many papers in use will be foundto be somewhat oleophilic in nature. Most, however, are also somewhathydrophilic. it is preferred, therefore, to standardize theoleophilic-hydrophobic character of the conductive base by impregnatingone surface thereof as shown at 18, with a composition consisting of anappropriate oleophilic filler such as zinc oxide, ground in vanysuitable oleophilic binder, for example nitrocellulose lacquer. I havefound that this treatment provides a surface on the conductive sheetwhich, when subjected to an electric current, has a definite oleophilic.tendency of a magnitude within limits which are the most suitable forthe purpose intended, and which is likewise suitably substantiallyhydrophobic.

When the conductive and oleophilic characteristics of the sheet 1612have been established in accordance with the above description, the sameis then covered on its oleophilic surface with a coating 17b of amaterial which is hydrophilic and at the same time susceptible of beinglocally disintegrated and disperwd in response to the passage of normalelectric recording currents therethrough. Such currents are usually inthe neighborhood of to 30 milliarnperes at an impressed voltage of 100to 300 volts. An example of the coating material suitable for thispurpose is one having a base of carboxymethyl cellulose, or a metallicsalt of the same which has been applied to the web and insolubilizedthereon. Preferably the coating further includes plasticizing agents,fillers, and, prior to its application, suitable volatile drying agents.A filler of zinc sulphide, zinc oxide, titanium dioxide, leadthiosulphate or a mixture thereof is found to be a beneficialconstituent of the coating 17b in that the same has the effect ofrendering the coating locally removable in a positive and precise mannerwhich makes for improved quality in the image produced. The exact effectof the use of such fillers in the hydrophilic coating is not at presentknown, but it appears that they have a tendency to reduce sofewhat thehigh resistance that a coating of this character would normally have,and thus start a reliable current flow across the coating which breaksthe same down and disperses it. Likewise the presence of the fillerparticles appears to partially interrupt the coating continuity in sucha Way as to render the coating somewhat more friable, whereby thedisruptive forces of the electric discharge are permitted to effect aready separation and dispersal thereof in well-defined areas.

A solution which has been successfully employed to form the locallyremovable coating 17b and which represents the form presently preferredis as follows:

Formula I Ingredients Parts by Weight Sodium carboxymethyl cellulose 3Zinc oxide 9 Titanium dioxide 1 Glycerine 3 Methanol 30 Water 65 Thesolution represented in Formula I above is spread on the sheet 26b anddried to form the coating 17b. Normally the same will then be treatedwith heavy metal salt solutions or in any other appropriate manner,depending upon the ingredients used, to render the same insoluble inwater while remaining hydrophilic.

This formula is given purely by way of example and not limitation andwill serve as a rough approximation of the proportions of the varioustypes of ingredients used when equivalents therefor are substituted.

For example various planographic surfacing materials of hydrophilicadhesive character will be found which can be readily substituted forthe sodium carboxymethyl cellulose, the thickening or film-formingingredient of the above formula. Some of the materials which can be usedin this fashion are cellulose glycollic acid, i.e. carboxymethylcellulose as Well as other alkali salts and the aluminum salt thereof.Furthermore other polysaccharide carboxy ethers such as those of starch,gum arabic, gum tragacanth, mesquite gum and larch gum will also proveto be useful. Alginic acid and salts thereof, as well as alkali salts ofdibasic acid styrene copolymers, will be found to be useful in thisconnection. While not to be preferred over the foregoing, polyvinylalcohols, urea aldehyde condensation products, gum arabic, gelatin andproteinaceous materials such as casein will also be found to beoperative for the purpose when placed in water solutions, spread andthen rendered insoluble with a suitable coagulant.

When a plate b constructed in this manner is placed on a platen 2b withits conductive surface in intimate contact therewith and when theenergized stylus 32 is engaged with the coating 17b the portion of thecoating directly beneath the stylus point is disintegrated and removedin response to the flow of electric current in the making circuit withthe result that a portion 34 of the oleophilic web is exposed. When theinscription of the plate 15b has been completed it is removed from theplaten 20 and appropriately mounted on a planographic printing presswhere the background formed by the remainder of the coating 17b iswetted and made ink-repellent and the portions 34 receive the oleousink, so that copies may be made therefrom in the usual manner.

While the coating 17b is described as hydrophilic, it is to beunderstood that the same preferably consists of a material capable, inand of itself, of forming a planographic surface in the usual manner,i.e. a surface having a hydnophilic-oleophilic balance suitable fordirect-imaging planographic work. By this is meant a surface which whendry is capable of accepting and retaining a 'waxy or other image-formingmaterial 35 having an affinity for oleous printing ink and repellingmoisture from the parts covered thereby, the remainder of the surface,or background, being still hydrophilic and capable of being moistened tosuch an extent that it will fail to pick up ink during printing. It ispointed out that the coating which employs carboxymethyl cellulose andany of the various substitutes described above is of this character andthe use of the same, or of other coating materials having equivalentproperties, is consequently preferred. The reason for this is that sucha coating not only acts in the manner of a locally dispersiblehydrophilic coating to form the main image due to localized removal byelectrical inscription, but the surface may also carry any auxiliaryimage which it is desired to add by the usual pressure transfer ofink-receptive material thereto as indicated by reference character 35-in FIG. 1.

The invention as illustrated in FIG. 1 and described above sets out theremovability or facsimile feature, and the hydrophilic or planographicfeature, as being combined in the coating 17!), but it will beunderstood that the invention also comprehendsthe incorporation of thesefeatures in separate coatings if found convenient or desirable. As shownin FIG. 2, a plate is constructed by providing the conductive paper 16bwith the oleophilic standardizing coat or impregnation 18 as previouslydescribed. To this surface is then applied a facsimile coating 1171?which is disruptable by the electric current passage and which mayconsist of a dispersion of a suitable filler in a film former. Anexample of an appropriate solution for this purpose is given by theimmediately following formula:

Formula 11 Ingredients Parts by Weight Zinc sulphide 40 Methocel (Methylcellulose 15 cps. mfg. by

Dow Chemical Co.) 2.5 Water 100.

In place of zinc sulphide, may be used zinc oxide, titanium dioxide orlead thiosulphate, or mixtures of two or more of these ingredients.

When the coating 1171) has been placed and dried, a thin planographiccoating 217 b is placed thereover which may be composed, for example, asset out in the following preferred formula:

heated, it becomes water insoluble and forms the water receptivebackground for planographic printing.

Another convenient manner in which the planographic coating 21715 may beapplied is by coating the surface of the plate with a 5% aqueoussolution of sodium carboxyethyl cellulose, drying, and theninsolubilizing the same by treating with an aqueous solution of coopersalts, aluminum salts, iron salts and chromium compounds in the ratio ofabout 6:2: 1: 1 respectively.

As explained for the form of the invention illustrated in FIG. 1 thestated formulas for coating 21712 give excellent results and arepresently preferred, however, planographic coatings based on thehydrophilic adhesive film formers previously listed may be substitutedwith somewhat similar effect.

Inscription of plate 115%; is conducted in the same manner as that forplate 151) in FIG. 1, and local removal of portions of coating 11717 dueto the electric current passed by the stylus will, it has beendiscovered, also cause the simultaneous disruption and removal of theoverlying portions of the coating 217b, and only such overlyingportions, to produce image areas such as 134.

While the placing and insolubilizing of the coating 17b, or of thecoating 217!) have been described as occurring prior to recording, theinvention also comprehends the preliminary inscription of the sheet bymeans of the electric current in the facsimile machine, and thesubsequent casting of the planograpnic coating which attaches itselffirmly to the background areas of the sheet. The image 34, i.e. thoseportions of a sheet 16b, 18 which were disrupted by current passage,provides a surface area which, for some reason not entirely understood,is not so readily covered by the aqueous coating solution used forforming the coating 7b as is the smooth undisturbed background surface.The disrupted areas thus reject it, at least in part, or at leastprovide some oleophilic fibrous protrusions above the coating capable ofaccepting ink even after wetting in the usual planographic printingprocess. In the case of the form of the invention shown in FIG. 2, thefacsimile coating 117 b may be placed prior to inscription by therecording current and locally removed thereby, and the planographiclayer 2171) may be formed afterwards to provide a hydrophilic masksurrounding the image and rendering the sheet capable of printing copieson a planographic printing press.

lVhile the plates b and 1151; illustrated in FIGS. 1 and 2 are adaptedfor use as conductive elements in a closed circuit type of facsimileapparatus, it will be understood that the same may be used equally aswell with space discharge or corona type of apparatus as ilustrated insaid Cooley Patent No. 1,702,595.

For many reasons it is often preferred to employ the corona or spacedischarge type of facsimile equipment, and the following embodiments ofthe invention are intended primarily for use therewith and are atpresent preferred. As seen in FIG. 3, such equipment may include arecording drum 2% which may be either conductive or nonconductive, andif the former, is usually provided with an insulating surface layer 120.Spaced from the drum far enough to be slightly removed from contact withany sheet mounted thereon is a stylus 32 which is electrically connectedto a high voltage, high frequency source 33. The record and master sheetmaking up this form of the invention is indicated generally by numeral150 and includes a foundation sheet 160 of paper which is preferablynonconductive since the cost of papers specially treated or speciallymade to have conductive properties throughout is relatively high. Thesheet may have a wet stren th treatment such as melamine formaldehyde ifdesired, but for very short printing runs of a few copies only, thisfeature is not entirely essential. To one surface of the paper fee isapplied a coating 18s of conductive material which provides a member orstratum for regulating the potential gradient and rendering it uniformover the entire surface of the sheet. This provides for properlycontrolled and uniform dispersion forces on the facsimile layer. Thelayer 18c is preferably a coating of substantial body and thickness ascontrasted with the impregnation 13 of FIGS. 1 and 2, and itsconductivity is relatively high. The layer 18c also includes a binderwhich has a sizing and fiber-laying effect on the material of the base160. A number of appropriate materials are available for this purpose,among them are starch, casein, water soluble gums such as gum arabic andmethyl cellulose. After the coating lic has been placed, the sheet willpreferably be partially dried and calendered to further lay the fibers.The filler content of the coating 18c will normally serve to furnish theconductive property, and to this end will usually be composed of finelydivided carbon, e.g. gas black. The presence of the carbon filler in thecoating will tend to render the same somewhat oleophobic as well, for apurpose which will presently appear.

It will be noted that the binders used in forming the coating 18c areall water dispersible, and this is to be preferred since it provides forapplication of the coating 13c directly on the initial pass through thepaper making machine, thus making possible important savings in the costof the sheet.

To the surface of the coating are applied coatings 117b and 21712 whichare substantially identical with the facsimile and planographic coatingspreviously described for FIG. 2 and may also be considered to beconstituted according to Formulas II and Ill respectively, or theirequivalents as previously stated.

When a plate is constructed according to the immediately foregoingdescription, and as shown in FIG. 3, and is subjected to facsimileprinting inscription by a stylus 32', it is found that the coatings11711 and 21712 are locally removed to provide image areas 234. Theareas 234 are portions where the coating 1180 is exposed, and it hasbeen discovered that these image areas have especially importantproperties, for in addition to being primarily oleophilic and inkreceptive, the surface of the conductive coating 18c appears to beexposed without substantial disruption of the fibers of the sheet lids.In the case of planographic sheets which have been heretoforeelectrically inscribed the projecting paper fibers which have erupteddue to current action have tended to make the image areas temporarilyabsorptive so that the copies printed have not always been clear andsharp, especially at the beginning of the printing run and before theimage has had a chance to become well inked and thus fully repellent tomoisture. According to the embodiment illustrated in FIG. 3, however,the fibers are well laid and firmly retained by the conductive coatingwhich by its presence and conductive properties seems to prevent thestylus discharge from disruptively affecting the surface fibers of thepaper sheet 16c. Thus the image areas avoid the initial partiallyabsorptive condition which would allow them to become partially andtemporarily wetted, and are fully ink receptive from the beginning ofthe printing run. This is an important feature inasmuch as the number ofcopies usually required from plates of this sort is small, and it isimportant that good copies be produced at the start in order to avoid ahigh percentage waste of copy sheet paper. Furthermore, the absence offiber ends at the image surface gives copy which is even much sharperand clearer than the ultimate image after it is well developed and wellinked when formed on a plate lacking the fiber-laying and conductivelayer 180.

While the form of the invention shown in FlG. 3 has been discussedprimarily in connection with the space discharge or corona type offacsimile operation, it will be understood that if desired and if thecost is warranted, the sheet He may also be made conductive like thesheet 162: for use in a conventional circuit type of facsimileinscription as illustrated generally in FIG. 1.

While the invent-ion has been described as useful with normal facsimileequipment with the inference that it is to be operated in a conventionalmanner to provide planogrhaphic masters or plates imaged with mattersent from a remote sending instrument, it will be understood that otheruses of the invention are also contemplated. For example, it has beenfound convenient in some instances to employ both sending and receivingfacsimile equipment at one location as a means for making a plate ormaster which, While an unchanged duplicate of an original, does notrequire photographic processes, thus avoiding the inconvenience,complications and usual messiness of timed exposures, developingsolutions, fixing treatments, drying and the like. It has been found,for example, that by adjusting the transmitting and recording speeds thecharacter definition can be adjusted so that line drawings and halftoneswill be reproduced giving masters which provide copies of excellentquality substantially approaching the clarity and definition obtainableby use of a planographic master produced by the ordinary photographicimaging process even under the most favorable circumstances.

Variations and modifications may be made within the scope of the claimsand portions of the improvements may be used without others.

I claim:

1. An electrically inscribable lithographic printing plate comprising aWet-strength electroconduct-ive paper base having an impregnation on onesurface thereof to render said surface oleophilic, said impregnationcontaining an oleophilic binder material and an oleophilic filler as theessential ingredients thereof, and, on the surface of said impregnation,an adherent electrically-removable coating of such character as to burnaway in elemental areas by the application of marking currents thereto,said coating containing as the essential ingredients thereof awater-dispersible adhesive binder material and a filler selected fromthe group consisting of zinc sulphide, zinc oxide, titanium dioxide,lead thiosulphate and mixtures thereof; and having adhered to thesurface of said electrically-removable coatin a thin water-insolublehydrophilic lithographic surface coating containing as the essentialingredients thereof a hydrophilic colloid and an insolubilizing agentfor said colloid; the said electricallyremovable coating being removableduring the inscribing of the lithographic printing plate by an electriccurrent whereby the overlying areas of the lithographic surface coatingare also removed, and the oleophilic impregnation being not removable bythe electric current.

2. An electrically inscribable lithographic printing plate comprising awet-strength electroconductive paper base having an impregnation on onesurface thereof to render said surface oleophilic, said impregnationcontain ing nitrocellulose binder material and Zinc oxide filler as theessential ingredients thereof, and, on the surface of said impregnation,an adherent electrically-removable coating of such character as to burnaway in elemental areas by the application of marking currents thereto,said coating containing as the essential ingredients thereof a methylcellulose adhesive binder material and a filler selected from the groupconsisting of zinc sulphide, zinc oxide, titanium dioxide, leadthiosulphate and mixtures thereof, and having adhered to the surface ofsaid electrically-removable coating a thin water-insoluble hydrophiliclithographic surface coating containing as the essential ingredientsthereof a carboxymethyl cellulose compound and an insolubilizing agentfor said compound; the said electrically-removable coating beingremovable during the inscribing of the lithographic printing plate by anelec tric current whereby the overlying areas of the lithographicsurface coating are also removed, and the oleophilic impregnation beingnot removable by the electric QUITHL 3. An electrically inscribablelithographic printing plate comprising a Wet-strength paper base havingan electrically-conductive and oleophilic coating adhered thereto, saidoleophilic coating containing as the essential ingradients thereofelectrically-conductive carbon and an adhesive sizing which lays andretains the surface fibers of the paper base even when the plate issubjected to marking current discharge, and, on the surface of saidoleophilic coating, an adherent electrically-removable coating of suchcharacter as to burn away in elemental areas by the application ofmarking currents thereto, said coating containing as the essentialingredients thereof a water-dispersible adhesive binder material and afiller selected from the group consisting of zinc sulphide, zinc oxide,titanium dioxide, lead thiosulphate and mixtures thereof, and havingadhered to the surface of said electrically-removable coating a thinwater-insoluble hydrophilic lithographic surface coating containing asthe essential ingredients thereof a hydrophilic colloid and aninsolubilizing agent for said colloid; the said electrically-removablecoating being removable during the inscribing of the lithographicprinting plate by an electric current whereby the overlying areas of thelithographic surface coating are also removed, and the oleophiliccoating being not removable by the electric current.

4. An electrically inscribable lithographic printing plate comprising awet-strength paper base having an electrically-conductive and oleophiliccoating adhered thereto, said oleophilic coating containing as theessential ingredients thereof electricallyconductive carbon and anadhesive sizing which lays and retains the surface fibers of the paperbase even when the plate is subjected to marking current discharge, and,on the surface of said olcophilic coating, an adherentelectrically-removable coating of such character as to burn away inelemental areas by the application of marking currents thereto, saidcoating containing as the essential ingredients thereof a methylcellulose dispersible adhesive binder material and a filler selectedfrom the group consisting of zinc sulphide, zinc oxide, titaniumdioxide, lead thiosulphate and mixtures thereof, and having adhered tothe surface of said electrically-removable coating a thinwater-insoluble hydrophilic lithographic surface coating containing asthe essential ingredients thereof a carboxymethyl cellulose compound andan insolubilizing agent for said comound; the saidelectrically-removable coating being removable during the inscribing ofthe lithographic printing plate by an electric current whereby theoverlying areas of the lithographic surface coating are also removed,and the clanphilic coating being not removable by the electric current.

References Cited in the file of this patent UNITED STATES PATENTS1,221,780 Wald Apr. 3, 1917 2,251,742 Kline Aug. 5, 1941 2,291,673Albers et al. Aug. 4, 1942 2,311,889 Toland et al. Feb. 23, 19432,313,497 Adrian Mar. 9, 1943 2,398,779 Dalton ct al. Apr. 23, 19462,494,053 Mitson et al Jan 10, 1950 2,554,017 Dalton May 22, 19512,555,321 Dalton et al. June 5, 1951 2,649,372 Hills Aug. 18, 1953FOREIGN PATENTS 550,575 Germany May 12, 1932 UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No .3 113 512 December 10 1963 DouglasA. Newman It is hereby certified that error appears in the abovenumbered patent requiring correction and that the said Letters Patentshould read as corrected below.

Column 3 line 16, for "sofewhat" read somewhat line 39, for "26b" read16b same column 3 line 73 for "making" read marking column 5 line 1 for"cooper" read copper line 44, for "ilustrated" read illustrated column 6lines 11 and 12 for "oleophobic" read oleophilic line 72 for"planogrhaphic" read planographic column 8 line 45 for "comound" readcompound Signed and sealed this 12th day of May 1964.

SEAL) ttest:

ERNEST W, SWIDER EDWARD J BRENNER Attestmg Officer Commissioner ofPatents

1. AN ELECTRICALLY INSCRIBABLE LITHOGRAPHIC PRINTING PLATE COMPRISING AWET-STRENGTH ELECTROCONDUCTIVE PAPER BASE HAVING AN IMPREGNATION ON ONESURFACE THEREOF TO RENDER SAID SURFACE OLEOPHILIC, SAID IMPREGNATIONCONTAINING AN OLEOPHILIC BINDER MATERIAL AND AN OLEOPHILIC FILLER AS THEESSENTIAL INGREDIENTS THEREOF, AND, ON THE SURFACE OF SAID IMPREGNATION,AN ADHERENT ELECTRCALLY-REMOVABLE COATING OF SUCH CHARACTER AS TO BURNAWAY IN ELEMENTAL AREAS BY THE APPLICATION OF MARKING CURRENTS THERETO,SAID COATING CONTAINING AS THE ESSENTIAL INGREDIENTS THEREOF AWATER-DISPERSIBLE ADHESIVE BINDER MATERIAL AND A FILLER SELECTED FROMTHE GROUP CONSISTING OF ZINC SULPHIDE, ZINC OXIDE, TITANIUM DIOXIDE,LEAD THIOSULPHATE AND MIXTURES THEREOF; AND HAVING ADHERED TO THESURFACE OF SAID ELECTRICALLY-REMOVABLE COATING A THIN WATER-INSOLUBLEHYDROPHILIC LITHOGRAPHIC SURFACE COATING CONTAINING AS THE ESSENTIALINGREDIENTS THEREOF A HYDROPHILIC COLLOID AND AN INSOLUBILIZING AGENTFOR SAID COLLOID; THE SAID ELECTRICALLYREMOVABLE COATING BEING REMOVABLEDURING THE INSCRIBING OF THE LITHOGRAPHIC PRINGTING PLATE BY AN ELECTRICCURRENT WHEREBY THE OVERLYING AREAS OF THE LITHOGRAPHIC SURFACE COATINGARE ALSO REMOVED, AND THE OLEOPHILIC IMPREGNATION BEING NOT REMOVABLE BYTHE ELECTRIC CURRENT.